1. Field of the Invention
The present invention relates to a fluorescent ink capable of forming a fluorescent image, and a recording unit, an ink cartridge, an ink-jet recording method, and an ink-jet recording apparatus employing the fluorescent ink.
2. Related Background Art
In ink-jet recording, the ink is ejected by utilizing various methods such as attraction by electrostatic force, mechanical vibration or displacement from a piezo element, pressure caused by bubbles formed by heating the ink, and so forth. In recent years, inks are required to be useful for ink-jet recording in various application fields. In such application fields, various techniques are disclosed not only for forming beautiful color images but also for forming fluorescent images for recording information such as characters, numerals, symbols, and bar codes on a recording medium to record non-visible information (e.g., security information). The fluorescent inks are promising in various application fields, so that development of the fluorescent ink which has high stability, high reliability, and high fluorescence developability is awaited. Inks containing a coloring materials having fluorescence developability (hereinafter, fluorescent coloring materials) disclosed in Japanese Patent Application Laid-Open Nos. 8-151545, 9-132729, 10-193775, 10-298462, and 10-298467; and Japanese Patent No. 233038. Various new recording methods and fluorescent coloring materials are disclosed therein.
The use of a fluorescent coloring material is disclosed, for example, in Japanese Patent Application Laid-Open Nos. 5-293976, 6-191143, 6-322307, 7-009755, 7-305013, 8-053639, 9-003375, 9-01294, 9-137097, 9-137098, 9-137099, 9-165539, 9-241565, 9-255904, 9-286939, 10-007962, 10-183043, 11-080639, 11-320921, and 2000-038529; and Japanese Patent No. 2995853.
The water-soluble fluorescent dye useful as a component of the aqueous fluorescent ink includes C.I.(Color Index No.) Basic Red 1, C.I. Basic Red 2, C.I. Basic Red 9, C.I. Basic Red 12, C.I. Basic Red 13, C.I. Basic Red 14, C.I. Basic Red 17, C.I. Acid Red 51, C.I. Acid Red 52, C.I. Acid Red 92, C.I. Acid Red 94, C.I. Basic Violet 1, C.I. Basic Violet 3, C.I. Basic Violet 7, C.I. Basic Violet 10, and C.I. Basic Violet 14.
Of these dyes, C.I. Acid Red 52, which comes to be excited at an excitation wavelength of about 260 nm to fluoresce at wavelength of 580–640 nm, is especially useful as the coloring material of a fluorescent ink for ink-jet recording, since this dye produces intense fluorescence, having high water-solubility, and causing little problem in safety in comparison with other fluorescent basic dyes.
C.I. Acid Red 52, however, is extremely poor in water resistance. Upon contact with water, the prints recorded with a fluorescent ink-jet recording ink containing such a dye, may lose the characteristic fluorescence, or the printed information may be completely vanished.